Carrier wave printing telegraph system



March 17, 1936 p ow L- v 2,033,948

CARRIER WAVE PRINTING TELEGRAPH SYSTEM Filed Jan. 9, 1954 2 Sheets-Sheet l Fal PERCI/WL 0. Low/51.4

1P. D. LOWELL 2,033,948

Filed Jan, 9,- 1934 2 sheets-sum 2 u V .R 5 M V 0. Q w R u w a Q w w 0 v 0 u u h M m L n \M ,3 m m U n U W a w H mm \m mm \M; b% \M. M u H CARRIER WAVE PRINTING TELEGRAPH SYSTEM March 17, 1936.

. "Patented Mar- 1 3 PATENT *OFFICEP."

2.033.948" cannin wave rnm'rmo mom. SYSTEM Percival n. Lowell, Chevy ChasqMd. f

My invention relates broadly to high-frequency signaling and more particularly to high trequency printing telegraph systems.

larly to a systemv known as "two tone", wherein the transmitter transmits a continuous, high frequency carrier wave modulated alternately by two'audio frequencies, one audio frequency be- 10 ing transmitted on the mark impulse and the other audio frequency being transmitted on the 'space impulse of the code symbols constituting the transmitted characters.

Heretofore, the ordinary method of two-tone '15 transmission has been effected by employing two sources of audio frequency energy, and connecting the outputs of these two sources alternately into the transmitter to modulate the high frequency carrier wave. has heretofore been accomplished by use of a mechanical relay, the contact system of which is arranged to operate as a'single pole double throw switch, so-that when the relay keying contacts are open, for instance, the relay tongue rests on one side, thereby connecting in the audio source of one frequency; and when the keying contacts are closed, the relay tongue throws to the other side, thereby connecting in the audio source of'the other frequency; The inherent defeet of prior systems of this character is that 'there is an appreciable period of time required for the relay tongueto travel from one side to the other, thereby introducing a distortion of the timing of the original impulses sent from the keying contacts.

It will be appreciated by anyone skilled in the art, that any distortion of impulses at the trans mitter must be corrected by intentionally distorting the relay adjustments at the receiving 40 station and after this is done, the receiving station relays will not be correctly adjusted to respond to the impulses received from a second transmitter which will have a still difierent amountof distortion in the timing of impulses '45 sent out. Thus, it'is advantageous to. eliminate all distortion of the length of impulses at the source, namely the transmitter, by eliminating all relays. v

One object of my invention is to provide a cir- 50 cuit arrangement for transmitting alternately two audio frequency'tones without the use 'oi-a circuit interrupting relay.'-

Another object of my invention is to provide a control system for a printingtelegraph trans- 55 mitter in which separate sources or audio fremitted signaling impulses.

This alternate connection Application January 9, 1934, Serial No. 705,963 scams. (0!. m-cs) quency energy are rendered alternately-eflective upon a high frequency carrier wave for modulating the carrier wave according to the separate My invention is directed to high frequency cart 5 rier current printing telegraph systems, particuaudio frequencies. without distorting the trans- 5v .A further object of my invention is to provide a system for effecting instantaneous control of a printing telegraph transmitterby changing the grid bias of a pair of electron tubes.

-' Other and further objects of my invention 10 reside in the circuit -arrangements more fully described in the specification by reference to the accompanying drawings, in which:

Figure 1 is a schematic wiring diagram of a circuit arrangement embodying the control means 15 of my invention in connection with a pair of audio frequency oscillating electron tubes; Fig. 2

-is a schematic diagram showing a modification of Fig. 1 in which the. control means of my'invention is connected with a pair of electron tube 20 audio frequency amplifiers; Fig. 3 is a diagram of the arrangement of the receiving apparatus for decoding the signals transmitted by the system-sh0wn in Fig. 1 or Fig; 2; and Fig. 4 is a graph showing the manner of variation of the. 5

frequency with respect to time under control or the means of my invention. v Fig. 1 shows one embodiment of my invention,

where l and 2 designate electron tube audio frequency oscillators which may have anyconven- 3o tional circuit arrangement, preferably, one which offers the greatest frequency stability. Reference characters 3 and 4 designate coupling means to couple the grid and plate circuits for producing sustained oscillations. Reference characters 5 and 35 j 6' indicate pick-up windings to couple the output of the two audio frequency oscillators l and 2 into a common audio frequency amplifier 1 whichin turn'is used to modulate the high frequency transmission system 8. For purposes of illustrao -tion, I have shown my'invention applied to a radio transmission system having an antenna I9 andground system 20, although'itwill be understood that I may apply the system of my invention to carrier wave line wire systems with equally eflicient results. Electron tubes l and 2 have .bias resistors! and I0 connected in their respective cathode return circuits. The keying circuit may consist of an automatic transmitted having a plurality of control contacts, as shown at l I. Thesecontacts are, connected so that they alternately make and break asho'rt circuit across bias resistor 9, according to thesequence of signaling impulses desired, The contacts ll represent the control contacts'oi a printing-telegraph transas and difierent tones, depending upon whether contacts.

for tube 2 is obtained through the voltage drop of both resistors 9 and I9 in series, but resistor I0 is of such high value as to have the same voltage drop as resistor 9, so that with'the arrangement shown in Fig. 1, the voltages across the two resistors are connected in series opposing,

therefore, the resultant grid bias of tube 2 is sub.-

stantially zero, and tube 2 will oscillate at its predetermined audio frequency. This audio energy is then fed through pick-up coil 6 in series with pick-up coil 5 into the audio amplifier! and thence into 8 to modulate the radio frequency carrier.

When sending, the contacts are closed, resistor 9 isshort circuited, the grid bias of tube 2 becomes highly negative because the bucking voltage across. resistor 9 has been shorted out, and tube 2 stops oscillating. Simultaneously, the grid bias of tube I is reduced to substantially zero so that now tube I oscillates at its predetermined audio frequency, and its output is fed through pick-up coil 5 in series with pick-up coil 6, into amplifier l, and modulates the carrier of transmitter 9. Bleeder resistors I2 and I3 operate to hold the voltage drop across resistors 9 and It more constant. Thus, the two tubes I 2, alternately generate audio frequencies of are closed or open, and without any appreciable time lag, as is the case when an electromagnetic relay is used.

Fig. 2 shows another embodiment of my invention wherein tubes 2| and 22 are used as audio frequency amplifiers. Reference characters I4 and I5 designate audio frequency generators, preferably of the tuning fork type, with their outputs coupled into the inputs of tubes 2| and 22, respectively. Upon closing the key contacts II, bias resistor 9 is short circuited and the grid bias of tube 2| is optimum for amplification due to the voltage drop across resistor I6 and the audio power from generator I4 is amplified by tube 2| and passed through coupling device and pick-up coil 5 in series with pick-up coil 6 into' amplifier I and thence into transmitter 8, modulating the carrier at the frequency of audio frequency generator I 4. Simultaneously, when contacts II are closed, tube 22 is biased highly negative to cut oil by the grid bias voltage drop across its cathode resistor III, and therefore, the audio frequency from audio frequency generator I5 is not passed by tube 22 and does not enter the amplifier I and transmitter 9. When contacts I I are opened, the operation is reversed, because then the grid of tube I receives the whole voltage drop across resistors 9 and it which is sufficient to bias tube I to cut off, thereby stopping the passage of audio frequency energy from audio frequency generator I4 into amplifier I and transmitter 8. At the same instant that contacts II are opened, the grid of tube 22 receives the difference in bias voltage induced across resistors 9 and I9 in series. The resistors 9 and III having such relative values that the difference in bias results in tube 22 receiving an optimum value of grid bias for best amplification and audio frequency from audio frequency generator I5..is passed through tube 22 through coupling device or pickup coil 6 in series with the coupling device or pickup coil 5, thence into amplifier I for modulating transmitter 8 at the audio frequency. of audio frequency generator I5.

In this manner, depending on whether contacts II are open or closed, tubes 2I and 22 alternately pass frequencies from audio frequency generators I4 and I5 into amplifier I and thence modulate the carrier of transmitter 8 altemately according to the sequence of contacting of contacts II. V

For purposes of simplification. I have not shown the cathode heating system in the accompanying drawings-but have merely indicated the essential elements of the tube such' as cathode, control grid and plate electrodes. I the several tubes has been indicated as a bat- Also' the plate supply for tery system; It will be understood that generators or rectified and filtered alternating current may be employed for the sources diagramvmatically illustrated. The bleeder resistors I2 and I3 become particularly important when the source of plate potential is not constant.

Fig. 3 shows the method which is employed for receiving and utilizing the energy transmitted by the system of Figs. 1 and 2. The radio frequency amplifier amplifies the signal as received and passes it to the detector which delivers the intermittent or successive impulses at the selected audio frequencies to parallel circuits, each of which comprises an audio frequency filter, am-

plifier and rectifier. The filters are separately tuned to respond to one of the impulse modulating audio frequencies, for example, as shown in Fig. 3, the upper filter passes the 1000 -signal and the lower filter passes the 1500 cycle signal. The outputs of the separate paths are connected to a polarized relay 24 whose movable tongue 25 carries the contactor 26 arranged to contact either of terminals 21 or 29 according as the signal impulse is l000- or 1500-. The terminals 21 and 29 and the contactor 26 through flexible connection 29 are connected to an automatic telegraphic printer.

Fig. 4 is a graph showing the nature of the signal and its variations with respect to time. The graph representsthe variations required for the formation of the letter B in accordance with the characters of the Baudot code. Seven impulses are required in the formation of every character, viz., an initial impulse for actuating the spacing mechanism of the printer, five consecutive impulses in varying combinations of two. audio frequencies for determining the character to be printed, and a final or stop impulse for effecting the printing of the character. I

Referring again to Fig. 1, tube I oscillates, for the purpose of explanation, at 1500 cycles per second and tube 2 at 1000 cycles per second, the

or 1500 cycles may be the normal operating sig-' nal frequency, and this normal frequency may be the spacer or printing impulse-the 1000 cycle normal frequency is used as the spacer impulse in the assumed case and is continuously transmitted when all keys are open. At the end of every sequence of letter forming impulses, howimpulses. Similarly,

ever, the other frequency impulse must always be transmitted to print the letter. The operation ofv the printer is well known in the art.

Fig. 4 shows the special'beneilt of applicant's system. The time lag caused by operation from the usual mechanical switching means at the transmitter, is shown at 30 at every change of signal frequency. This represents the lag that may be characteristic of one transmitter and varies with every relay. The disadvantages arising from this lag have heretofore been pointed-out, particularly the failure of a multiplicity of printers to follow a master transmitter which introduces inherent distortion in the transmitted a single printer fails'to follow a number of master transmitters because the time lag of each is different. The response in the system of my invention is shown as being instantaneous at 3| since the time of control of oscillations by change of the grid bias is practically instantaneous.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A control system for an automatic telegraph transmitter comprisinga pair of electron tube deivices having anode, cathode, and grid electrodes, symmetrical anode circuits connected with said electron tube deyices, and unsymmetrical grid biasing circuits having common resistor for selectively rendering operative one or the other of said electron tube devices.

2. A control system for a printing telegraph transmitter comprising a pair of audio frequency amplifying electron tubes having anode,- cathode, and grid electrodes, and input and output circuits, audio frequency generators connected to said input rical and connected to a high frequency transmission system, unsymmetrical grid biasing circuits having keying means shunting a common resistor for selectively rendering operative one or the other of said amplifying electron tubes.

3. A control system for a printing telegraph transmitter comprising a pair of audio frequency oscillating electron tubes having anode,- cathode, and control grid electrodes, a source of potential connected to said anode elements, means connected with said control elements and said source of potential for unequally biasing the control grids for effecting normal operation of one of said electron tube oscillators and preventing the action of the other of said electron tube oscillators, and

contact means for effecting normal operation of said formerly inactive electron tube oscillator and preventing the action of said formerly operative electron tube oscillator.

4. A control system for a printing telegraph transmitter comprising a pair of audio frequency oscillating electron tubes having anode, cathode, and grid'electrodes, symmetrical anode circuits connected with said tubes, and unsymmetrical gridvcathode circuits having in common contact keying means shunting a circuits, said output circuits being symmetmeans for selectively rendering operative one or the other of said oscillating electron tubes.

5. A control system for a printing telegraph transmitter comprising a pair of electron tube devices having anode. cathode, and grid electrodes, a source of potential, a pair of resistors connected in parallel across said source of potential,.one of said resistors connected in series with the cathode and grid electrodes of one of said electron tube devices, both of said resistors connected in series between the cathode and grid electrodes of the other of said electron tube devices, and keying means operating to shunt said one resistor and change the bias on the respective grid electrodes.

6. A control system for a printing telegraph transmitter comprising a pair of electron tube devices having anode, cathode and grid electrodes, symmetrical anode circuits, and unsymmetrical grid-cathode circuits connected with said electron tube devices, an electrical circuit element, connections from said electrical circuit element to each of said grid-cathode circuits, and contact means connected with taps on said electrical circuit element said grid-cathode circuits for shunting or unshunting said electrical circuit element and selectively rendering operative one or the other of said electron tube devices.

7. A control system for a telegraph transmitter comprising a pair of electron tube devices having anode, cathode and grid electrodes, symmetrical anode circuits and unsymmetrical grid-cathode circuits connected with said electron tube devices, a source of bias potential and contact means for simultaneously modifying the effect of said bias potential on the respective grid electrodes for selectively rendering operative one or the other of said electron tube devices.

8. A control system for a telegraph transmitter comprising a pair of electron tube devices having anode, cathode and grid electrodes, symmetrical anode circuits and unsymmetrical grid-cathode circuits connected with said electron tube devices, a source of negative bias potential and contact means for simultaneously changing the magnitude of negative potential impressed on the rei of bias potential and saidcontact means whereby said contacts when closed operate to impress a bias potential on the grid electrode of one of said electron tube devices for rendering it operative while simultaneously impressing a bias potential on the grid electrode of the other of said electron tube devices for rendering said last mentioned electron tube device inoperative.

PERCIVAL D. LOWELL. 

